Process for preparing jet fuels



United States Patent 3,201,345 PROCESS FOR PREEARING JET FUELS Harry A.Hamilton,'Natrona Heights, Alfred M. Heuke, Springdale, and Harry C.Staui'r'er, Cheswich, Pa, assiguors to Gulf Research & DevelopmentCompany, Pittsburgh, Pa., a corporation of Delaware No Drawing. FiledJune 14, 1962, Ser. No. 202,402

4 Claims. (Cl. 208-255) This invention relates to the preparation ofimproved jet fuels and in particular to the preparation of such fuels bya combination procedure involving hydrogenation and solvent extraction.

The jet fuels that are available commercially are not entirelysatisfactory. The requirements for a satisfactory jet fuel are numerousandare quite stringent; for instance, jet fuels must be used to cool jetengines. In other words, the jet fuel is passed through preheatersintegral with the jet engine in order to maintain the engine at a lowtemperature. Of course, the fuel is preheated in this manner, which isalso desirable. However, the amount of heat which must be removed isconsiderable, and this means that the jet fuel must be heated to hightemperatures during this preheating operation. Trouble has beenencountered due to deposition of carbon in the preheaters at these hightemperatures. Therefore, it is necessary to have a jet fuel which hashigh thermal stability. This is especially true in connection with jetsemployed in planes which fly at high Mach speeds where heat generationis excessive. Furthermore, jet fuelsare employed at high elevations andtherefore are subjected to unusually low temperatures. This means thatthe jet fuel must not freeze or deposit solids at these lowtemperatures; otherwise filters and injecting mechanisms would becomeclogged. Suitably high heats of combustion, i;e., high B.t.u. content,is also a necessity. Furthermore, a goodjet fuel should burn cleanly inthe jet engine. It is evident that the provision of high quality jetfuel is not a simple matter. This is particularly true if such a highquality jet fuel is to be available at a reasonable cost.

This invention has for its object to provide procedure for preparing animproved jet fuel. Another object is to provide economical procedure forpreparation of a high quality jet fuel. Other objects will appearhereinafter.

These and other objects are accomplished by our in vention whichincludes contacting a petroleum distillate boiling in the range betweenabout 250 and 550 F., having a freezing point below about 45 F., aviscosity at 40 F. below about 15 centistokes and composed primarily orpredominantly of paraflinic and/or naphthenic hydrocarbons with hydrogenin the presence of a hydrorefining catalyst. This contacting withhydrogen takes place at elevated temperatures and pressures suitable forhydrorefining of the feed stock without substantial cracking orconversion of the feed stock into lower boiling hydrocarbons. Thereafterat least part of the so hydrogen-treated product is extracted with apreferential solvent for aromatic hydrocarbons. A superior jet fuel isrecovered from the raflinate.

The feed stock to our improved process may be any petroleum fractionboiling in the range between about 250 and 550 F., provided that it hasa freezing point below about 45 F., a viscosity at -40 F. below about 15centistokes and is predominantly composed of paraffinic and/ ornaphthenic hydrocarbons. Thus heavy naphtha, kerosene or a mixture ofheavy naphtha and kerosene may be employed. It is advantageous toutilize distillates boiling in the above temperature range, whichdistillates are derived from parafiinic or naphthenic type crudes. Forinstance, Mid-Continental and Pennsylvania 3,201,345 Fatenied Aug. 17,1965 type crudes are suitable sources of feed stocks. We prefor toemploy feeds which boil in the range between about 330 and 515 F.

The catalyst employed in the hydrogen treatment may be any of thewell-known hydrorefining catalysts employed for treatment of petroleumfractions in order to hydrogenate olefins, hydrodesulfurize, etc.Examples of such catalysts are Group Vi left hand column or Group VIIImetals, oxides and sulfides. Mixtures of such Group VI and Group VH1metal oxides and sulfides are particularly advantageous. Specificexamples of suitable hydrorefining catalysts are molybdenum oxide orsulfide, tungsten oxide or sulfide, nickel oxide, nickel sulfide, cobaltmolybdate, nickel tungstate, amixture of nickel sulfide and tungstensulfide, etc. These catalysts are advantageously deposited upon an inertporous catalyst carrier such as activated alumina, the variousforms ofalumina such as gamma alumina and eta alumina and deactivated silicaalumina, etc. In the event that a carrier such as the last-mentionedcarrier is empl0yed,.it is necessary that the cracking activity bedestroyed since substantial cracking of the feed is undesirabie. Amountsof between about 5 and 25 percent by weight of hydrogenating componentmay be deposited on the carrier.

The hydrogen treatment described may be carried out at a temperature ofbetween about 500 and 800 F. and preferably between 600 and 725 F. Apressure of about to 2000 p.s.i.g. and preferably 500 to 1000 p.s.i.g.is employed. The temperature and pressure conditions are so selectedthat hydrogenation conditions prevail in the reactor and so that thereis hydrogenation of deleterious substances present in the feed stock.These deleterious substances are not all elucidated, but they appear tobe primarily gum-forming materials, olefins, sulfur compounds, nitrogencompounds, etc. While pressures higher than 2000 p.s.i.g. may be usedwith entirely satisfactory results, there is no particular advantage insuch higher pressures and, of course, they are more costly to employ. Aliquid hourly space velocity of between about 0.2 and 10.0 andpreferably between about 1 and 4- is employed. A hydrogen recycle rateof between about 5000 and 10,000 s.c.f./bbl. and preferably betweenabout 1000 and 3000 s.c.f./bbl. is utilized.

The abovementioned feed stock is contacted with the hydrogen and thecatalyst in any customary manner for hydrorefining of hydrocarbons. Themost usual procedure for this type of operation is to pass the hydrogenand vaporized hydrocarbon together through a high pressure reactor whichcontains a body of solid pieces of the hydrorefining catalyst. Thehydrogen and feed may be passed downwardly through the hydrorefiningreactor or upfiow therethrough. After passage through the reactor, thehydrogen is separated from the condensed hydrorefined hydrocarbon and isrecycled for re-use in known fashion.

It is advantageous at this stage to distill the hydrocarbon product fromthe hydrogen treatment. If the original feed stock contained onlycomponents boiling in the range of the desired jet fuel, then after thehydrogen treatment the hydrogen-treated product can. simply be subjectedto a low-cost topping operation to remove the small amount of volatilematerial formed during the hydrogen treatment. It is, of course,feasible to employ other procedures. For instance, an original chargestock boiling over a broader range than the desired jet fuel can behydrogenrefined, and then the desired jet fuel separated from thehydrogen-treated product. An alternative, but less desirable procedure,is to directly extract the hydrogen-treated distillate and then separatethe jet fuel portion therefrom.

We have found that any solvent which preferentially removes aromatichydrocarbons is useful for improving the hydrogen-treated fraction inregard to jet fuel charaoteristics. We do not know what materials areextracted by these solvents, but we have found that these solventsremove materials which are present in the hydrogentreated fraction whichhave a deleterious effect on the jet fuel properties. These are notnecessarily aromatic hydrocarbons as is pointed out above. Furfural is apreferred solvent for this purpose. However, examples of other suitablesolvents are diethylene glycol, dimethyl sul-foxide, ace-tonitrile andsulfur dioxide.

The solvent extraction is carried out in the same manner as employed inthe petroleum industry for solvent refining of petroleum fractions toremove aromatic constituents. The solvent ratios customarily employedfor such solvent extractions may also be used. In connection with thesolvents mentioned above, a solvent to oil ratio of :1 to 3.0 and atemperature of 70 to 150 F.; a solvent to oil ratio of 0.5 to 5.0 and atemperature of 100 to 170 F.; a solvent to oil ratio of 0.2 to 10.0 anda temperature of 70 to 170 F.; a solvent to oil ratio of 0.1 to 10.0 anda temperature of 40 to 140 F;. and a solvent to oil ratio of 0.1 to 3.0and a temperature of 20 to30 F. advantageously would be used forfurfural, diethylene glycol, dimethyl sulfoxide, acetonitrile and sulfurdioxide respectively. With other solvents, the solvent to petroleumfraction ratio should preferably be adjusted so that the maximum yieldof jet fuel is obtained having the desired specification-s.

After the solvent extraction has been completed, the ratfinate issubjected to treatment for removal of residual solvent. The mostadvantageous procedure for such removal will depend upon the solventemployed. In the case of furfural, conventional distillation orazeotropic distillation is preferred. After removal of residual solvent,the product constitutes the desired high quality jet fuel. Of course, ifthe original feed stock to the hydrogen treatment did not have thedesired boiling range for the jet fuel to be prepared or if the smallamount of volatile materials formed during hydrogen treatment were notremoved after the hydrogen treatment, then a distillation step isrequired after the solvent extraction to separate the desired jet fuel,i.e., the jet fuel having the required boiling range.

EXAMPLE A West Texas kerosene having the characteristics shown in TableI was contacted with hydrogen in the presence of anickel-cobalt-molybdenum-oxide catalyst deposited upon activated aluminaat a temperature of 650 F.; a pressure of 600 p.s.i.g.; a liquid hourlyspace velocity of 5.0; and a hydrogen recycle rate of between 1500 and1800 s.c.f./bbl. The hydrogen employed was 88 percent pure obtained froma hydroreforming operation. The resulting product was topped to removecomponents boiling below 325 F. and was then extracted with furfural ina ratio of one part furfural to four parts kerosene in a 15 stageSchiebel column at a temperature of 160 F. Thereafter the kerosene wassubjected to distillation to remove residual furfural. The product whichwas obtained in a yield of 90 percent had the properties shown in TableII.

Table I Gravity, API 42.6 Freezing point, F. 68.0 Viscosity at 40 F.: C11.76 Aromatics, vol. percent 19.1 Olefins, vol. percent 1.4 Sulfur,total wt. percent 0,448 Mercaptan sulfur, wt. percent 0.12 Nitrogen, wt.percent 0.003 Distillation Initial boiling point, F 314 End point, F.497 5 364 373 4 Table l-Continued DistillationContinued End point, F.:

Table II.-Pr0duct Gravity, API 44.7 Lbs/gal. 6.69 Viscosity at 40 F.: C11.18 Freezing point, F. -59 Sulfur, wt. percent 0.015

Mercaptans sulfur, wt. percent 0.0005

1. The process for preparing a jet fuel which comprises cont-acting apetroleum distillate having a freezing point below about -45 F., aviscosity at 40 F. below about 15 centistokes, which includessubstantial amounts of hydrocarbons boiling in the range between about250 and 550 F. which are composed predominantly of a member of the groupconsisting of parafinic and naphthenic hydrocarbons, with hydrogen inthe presence of a hydrorefining catalyst at a temperature between about500 and 800 F. at a pressure between about and 2000 p.s.i.g. and at aliquid hourly space velocity between about 0.2 and 10, said reactionconditions being selected within the specified ranges to result in thehydrogenation of the gum-forming materials present in the feed stockwithout substantial conversion of the petroleum distillate into lowerboiling hydrocarbons, and without substantial saturation of aromaticcompounds, extracting deposit-inducing substances from the hydrogenatedproduct with a solvent selected from the group consisting of furfural,diethylene glycol, dimethyl sulfoxide, acetonitrile, and sulfur dioxide,and recovering a jet fuel from the rafiinate.

2. The process for preparing a jet fuel which comprises contacting apetroleum distillate having a freezing point below about -45 F., aviscosity at -40 F. below about 15 centistokes, boiling in the heavynaphthakerosene range and composed predominantly of a member of thegroup consisting of parafiinic and naphthenic hydrocarbons, withhydrogen in the presence of a mixed Group VI-Group VIII hydrogenationcatalyst deposited upon an inert porous carrier at a temperature betweenabout 500 and 800 F. at a pressure between about 100 and 2000 p.s.i.g.and at a liquid hourly space velocity between about 0.2 and 10, saidreaction conditions being selected within the specified ranges to resultin the hydrogenation of the gum-forming materials present in the feedstock without substantial conversion of the petroleum,

distillate into lower boiling hydrocarbons, and without substantialsaturation of aromatic compounds, extracting deposit-inducing substancesfrom the hydrogenated product with furfu-ral and recovering a jet fuelfrom the rafiinate.

3. The process for preparing a jet fuel which comprises contacting apetrol-cum distillate having a freezing point below about 45 F., aviscosity at -40 F. below about 15 centistokes, boiling in the heavynaphthakerosene range and composed predominantly of a member of thegroup consisting of parafiinic and naphthenic hydrocarbons with hydrogenin the presence of a cobaltmolybdenum catalyst deposited upon activatedalumina at a temperature between about 600 and 725 F. at a a pressurebetween about 500 and 1000 p.s.i.g. and at a liquid hourly spacevelocity between about 1 and 4, said reaction conditions being selectedwithin the specified ranges to result in the hydrogenation of thegum-forming materials present in the feed stock without substantialconversion of the petroleum distillate into lower boiling hydrocarbons,and without substantial saturation of aromatic compounds, extractingdeposit-inducing substances from the hydrogenated product with furfuraland recovering a jet fuel from the raffinate.

4. The process for preparing a jet fuel which cornprises contacting apetroleum distillate, having a freezing point below about 45 F., aviscosity at 40 F.

6 below about 15 centistokes, having a boiling range between about 330and 515 F, and composed predominantly of a member of the groupconsisting of paraifinic and naph-thenic hydrocarbons, with hydrogen inthe presence of a cobalt-molybdenum-alumina catalyst at a temperaturebetween about 600 and 725 F. at a pres- References Cited by the ExaminerUNITED STATES PATENTS 2,731,506 l/56 Love et a1. 260683.9 2,846,358 8/58Bieber et a1. 208-212 2,967,204 1/61 Beuther et al. 260-667 3,077,7332/63 Axe et a1, 208212 3,098,106 7/ 63 Edwards 260-467 AL-PHONSO D.SULLIVAN, Primary Examiner.

1. THE PROCESS FOR PREPARNG A JET FUEL WHICH COMPRISES CONTACTING APETROLEUM DISTILLATE HAVING A FREEZING POINT BELOW ABOUT -45*F., AVISCOSITY AT -40*F. BELOW ABOUT 15 CENTISTOKES, WHICH INCLUDESSUBSTANTIAL AMOUNTS OF HYDROCARBONS BOILING IN THE RANGE BETWEEN ABOUT250 AND 550*F. WHICH ARE COMPOSED PREDOMINANTLY OF A MEMBER OF THE GROUPCONSISTING OF PARAFINIC AND NAPHTHENIC HYDROCARBONS, WITH THE HYDROGENIN THE PRESENCE OF A HYDROREFINING CATALYST AT A TEMPERATURE BETWEENABOUT 500 AND 800*F. AT A PRESSURE BETWEEN ABOUT 100 AND 2000 P.S.I.G.AND AT A LIQUID HOURLY SPACE VELOCITY BETWEEN ABOUT 0.2 AND 10, SAIDREACTION CONDITIONS BEING SELECTED WITHIN THE SPECIFIED RANGES TO RESULTIN THE HYDROGENATION OF THE GUM-FORMING MATERIALS PRESENT IN THE FEEDSTOCK WITHOUT SUBSTANTIAL CONVERSION OF THE PETROLEUM DISTILLATE INTOLOWER BOILING HYDROCARBONS, AND WITHOUT SUBSTANTIAL SATURATION OFAROMATIC COMPOUNDS, EXTRACTING DEPOSIT-INDUCING SUBSTANCES FROM THEHYDROGENATED PRODUCT WITH A SOLVENT SELECTED FROM TEH GROUP CONSITING OFFURFURAL, DIETHYLENE GLYCOL, DIMETHYL SULFOXIDE, ACETONITRILE, ANDSULFUR DIOXIDE, AND RECOVERING A JET FUEL FROM THE RAFFINATE.